This invention relates in general to wireless telecommunications networks and applications and, in particular, to a method and system of optimizing the signal strength of the network. More particularly, the invention relates to methods of determining cumulative clutter path loss between two points within the network.
Without limiting the scope of the invention, its background is described in connection with a wireless telecommunications network utilizing a matrix of bins to predict clutter signal losses in order to determine appropriate power levels, as an example.
Present-day mobile telephony has spurred rapid technological advances in both wireless and wireline communications. The wireless industry, in particular, is a rapidly growing industry, with advances, improvements, and technological breakthroughs occurring on an almost daily basis. Many mobile or wireless telecommunications systems, among them the European GSM-system, have passed through several generations of advancements and development phases. System designers are now concentrating on further improvements to such systems, including system refinements and the introduction of optional subscriber services.
Most wireless telecommunications systems are implemented as cellular telephone networks wherein a group of Base Transceiver Stations (BTSs), or base stations are served by a centrally located switch. The switch is commonly referred to as a Mobile Switching Center (MSC). The base stations are spaced apart from each other by distances of between one-half and twenty kilometers. Each base station is assigned a number of two-way voice and control channels. The voice channels transmit voice signals to and from proximately located mobile handsets, and transmit control information to and from these mobile handsets, usually for the purpose of establishing a voice communications link.
Calls by mobile subscribers can be affected by interference or radio disturbance events which, in turn, limit the efficiency of the network. As such, it is important to identify those cells within the network, which are sources of and subject to radio disturbance events. Interference itself can be either external or internal to radio network. The internal interference results from call activities within a network. In this regard, it is appropriate to term the cells as either xe2x80x9coffendingxe2x80x9d or xe2x80x9cdisturbed.xe2x80x9d Also, in this regard, a radio disturbance event typically occurs during a cellular call, either on the downlink (from a base station to a mobile handset) or on the uplink (from a mobile handset to a base station). The disturbance events include co-channel interference or adjacent channel interference. Similarly, different sources of external interference exist that can create problems in the network. Objects such as trees and buildings, for example, are known to those skilled in the art as xe2x80x9cclutterxe2x80x9d. Clutter affects a signal as the signal propagates through the objects.
Presently, methods and systems exist for identifying xe2x80x9cclutteredxe2x80x9d areas within wireless telecommunications networks. Typically, in a wireless network, when a signal propagates between a base station and a mobile handset, it often has to pass through many objects between the base station and the mobile handset.
In one method, in order to account for clutter within the coverage area including the base station and the mobile handset, the coverage area is subdivided into clutter areas. Each clutter area is then assigned an average clutter value which represents the types of clutter found within that clutter area. The signal strength between the base station and the mobile handset is then adjusted based on the clutter value for the clutter area in which the mobile handset is located. Thus, the signal is adjusted to accommodate the change in signal strength only due to the clutter in that specific clutter area. If, for example, there are large objects creating significant clutter in clutter areas along the path between the base station and the mobile handset, the prior art techniques of identifying clutter would not correctly account for this additional clutter. The validity of such predictions are dependent on a number of factors, including the accuracy of the propagation model utilized and the resolution of the terrain data, for example.
Another prior art clutter technique involves the use of interference prediction tools, along with trial and error, and xe2x80x9cdrive-byxe2x80x9d techniques to predict and measure the effects of changes in the radio network. These tools are useful in predicting where interference will effect the cellular system given a specific output power generated by the radio base station. The predictions are accurate only if the propagation model is accurate. The sources of interference can be identified, but again, the accuracy is a function of the propagation model. The drive-by methods, on the other hand, are quite accurate as they are based on clinical measurements, but require an immense amount of resources to implement.
Such tools are helpful in identifying the cells that have coverage and interference problems, but taken together are often inaccurate because of the dependence on predictions. That is, such prediction tools do not always account for xe2x80x9creal-lifexe2x80x9d sources of interferences in the coverage area as determined through more empirical measurement methods.
While prior art techniques are useful in identifying, predicting and measuring the effects of coverage and interference in the network, they do not suggest how clutter in one part of the network can effect the performance in another part. What is needed is a method of optimizing the methods for determining the effects of clutter on signal strength in a wireless telecommunications network. A means for predicting clutter signal loss in the coverage area of a network would provide numerous advantages.
The present invention provides a method and system for optimizing signal strength and minimizing interference in a wireless telecommunications network. With the present invention, once the network operator has identified the sources of clutter, such information may be used in improving performance of the network. That is, the clutter in all of the bins between a transmitter and a receiver is accounted for in adjusting the signal strength between a transmitter and a receiver to determine the cumulative clutter path loss.
Disclosed in one embodiment is a method of determining the cumulative clutter path loss between two points within a coverage area in a telecommunications network. Initially, the coverage area is divided into a geographical matrix of bins. Each bin represents a subset of the coverage area. The size of the bin can vary and is dependent on the resolution needed to obtain an accurate clutter value along the path.
Once the coverage area is divided, a clutter value is assigned indicating the appropriate losses a signal experiences as it propagates through a bin. In one embodiment, the clutter value is assigned by taking an average value determined by drive testing a bin to determine an average signal loss value. In another embodiment, the clutter value is assigned based on the objects in the bin. In yet another embodiment, the clutter value is calculated for each object that the signal path crosses through as it propagates through the bin.
Finally, the clutter values for each bin along a radial connecting the transmitter and the receiver are added together to create a cumulative clutter path loss value. The cumulative clutter path loss value is used to adjust the signal strength between the transmitter and receiver to account for all the significant objects along the path.
In another embodiment of the invention, a system for determining a cumulative clutter path loss between two points within a coverage area of a network is disclosed. The system comprises a means for dividing the coverage area into a geographical matrix of bins. The bins are used to allow for a better resolution of signal loss over the coverage area. The system further comprises a means for assigning a clutter value to each bin. The clutter value indicates the appropriate losses a signal experiences as it propagates through a bin. The system also comprises a means for adding the clutter values of the bins along a radial connecting two points in order to determine the cumulative clutter path loss. The two points are represented by a transmitter and receiver. In one embodiment, the transmitter is a base station and the receiver is a mobile handset. In another embodiment, the transmitter is a mobile handset and the receiver is a base station.
Disclosed in another embodiment is a program product for optimizing the signal strength between two points by accounting for the cumulative clutter between the two points. The program product is typically a software program used for carrying out the steps of the invention. The program product comprises an instructional means for dividing the coverage area into a geographical matrix of bins and an instructional means for assigning a clutter value to each bin indicating the appropriate losses a signal would experience as it propagates through a bin. The program product further comprises an instructional means for adding the clutter values of the individual bins along a radial connecting two points together. The two points are typically a transmitter and a receiver. In one embodiment, a base station and a mobile handset will function as a transmitter and receiver, respectively.
A technical advantage of the present invention includes more accurate propagation predictions for coverage interference. As such, the propagation analysis takes into account the behavior of all clutter between two points within the network rather than only the clutter of the terminal bin.
Another technical advantage of the present invention is enabling radio network engineers to optimize the network with the objective of minimizing interference.